Arc welding is defined as a group of welding processes wherein coalescence is produced by heating with an electric arc, with or without the application of pressure and with or without the use of filler metal. In all cases, an arc is maintained between an electrode and the work, or between two electrodes, which form the terminals of an electric circuit.
More than a heat source, the arc is a complex mixture of ionized gas particles accelerated through an electric field constricted by a magnetic field, and exerting a profound effect on the transfer of filler material. In turn, arc behavior is dependent on filler material and base metal as well as circuit characteristics.
In an arc welding circuit, the workpiece is generally held at or near ground potential while the arch electrode is maintained at a positive potential with respect to the workpiece. Electric discharge between the electrode and the workpiece occurs and the arc is defined.
The ground welding cable is connected to the workpiece by a ground clamp. Such clamp should furnish a strong positive connection, yet be capable of a quick, easy attachment and removal, to both the workpiece and to the welding cable. The clamp should also be capable of withstanding abuse.
Most ground clamps used in welding processes fall into one of two categories, either the clamp is a spring actuated clamp or is a screw actuated clamp. While each of these clamps has certain advantages, each also has certain drawbacks.
For example, the spring clamp is prone to degraded performance due to the wear and tear it is subjected to during use. The spring becomes loose, and the electrical contact between the clamp and the workpiece becomes spotty or loose. This is especially the case if the workpiece is dirty or is covered with grease or oil, as is often the case. An incomplete contact between the ground and the workpiece can result in arcing and heating. All of these results are undesirable, and can reduce the life of the welding apparatus as well as inhibit the quality of the weld being made.
For this reason, many grounding clamps use a screw operated mechanism to attach the clamp to the workpiece. While many of the problems associated with spring actuated clamps are overcome by the screw actuated clamps, these clamps also have certain drawbacks. For example, the electrical circuit between the ground cable and the workpiece on one side of the clamp mechanism may be different from the electrical circuit on the other side of the workpiece. Since the clamps generally have a certain resistivity, that is, resistance per unit length for a given cross sectional area, this difference in electrical circuits can result in a difference in resistance between one path and another. Such difference in resistance will create a heating effect due to i.sup.2 R heating. Such effect may generate heat that is transferred throughout the clamp and may degrade the overall performance of the clamp. Still further, most of the known screw operated clamps locate the screw mechanism in a position to be adversely affected by the energy generated by the arc. This can further degrade the performance of the clamp.
The use of the screw mechanism also does not have the quick action advantages of a spring operated mechanism, and thus can inhibit the use of the clamp.
The ground attachment is most efficient if it is established as close to the work area as possible. However, such close proximity to the arc may degrade the spring clamps, and may also be harmful to the screw actuated clamps since both types of clamps locate the operating mechanism close to the clamping area.
Therefore, there is a need for a welding ground clamp which forms a tight, proper grip close to the welding area and which evenly grounds all elements of the ground clamp, yet which will not significantly degrade over time and which is not subject to decreased performance due to dirt and the like on the workpiece as are present ground clamps.